I should point out, for clarity, that while the context of what happens with Saul and the medium suggests a very likely probability the real issue at hand of a soul that is separate from the body shouldn't be dismissed.
the fact is, as you pointed out, the bible isn't actuslly clear because translation into English leaves some things in doubt. Like in psalms it says that a persons spirit goes out before they go back to the ground (still haven't researched that yet), it also seems to indicate a separation in other areas which I can't think of off the top of my head. Then in the book of Enoch it specifically says that the souls of the dead go off into different... Sort of receptacles after death where they wait.
its a very interesting subject. But at least where Samuel is concerned, my response is likely the one you'll get from anyone still in- and unfortunately the context supports it. So a different angle, in my opinion, would be best- if intended to use on such people. And outside sources like those posited here will be ignored by those people. Thus, as you mentioned, studying the same bible they use for support (real and not created support) of possibilities to put forward is the best course imo.
also, it wasn't my intention to give offense, I just took what you said at face value. Something cannot supposedly be a thing in a case such as this- either it is or it is not. Your choice of verbiage suggests you either think it isn't or have serious enough doubts to use words that suggest it isn't (I.e., supposedly is a word that inherently casts doubt). And I'm not bothered either way whether you feel it is or isn't.